Buck converter with improved filter design

Abstract

A buck converter for use in controlling a motor in accordance with an embodiment of the present invention includes a power input operable for connection to a DC power supply, a switch for selectively connecting the motor to the power supply, a pulse width modulation controller operable to provide a pulse width modulation signal to the switch, wherein the switch connects the motor to the power supply based on the pulse width modulation signal, and a voltage shifting capacitor connected across the switch and in series with a diode. The buck converter may include a shift control device operable to control a voltage across the voltage shifting capacitor.

What is claimed is: 
     
       1. A buck converter for use in controlling a motor, the buck converter comprising:
 a power input operable for connection to a DC power supply; 
 a switch for selectively connecting the motor to the power supply; 
 a pulse width modulation controller operable to provide a pulse width modulation signal to the switch, wherein the switch connects the motor to the power supply based on the pulse width modulation signal; 
 a voltage shifting capacitor connected with an anode of a diode; and 
 another switch directly connecting said anode of said diode to aground terminal of said DC power supply; 
 wherein said voltage shifting capacitor and said diode are connected, in series, across said switch, and said diode is connected to said motor only at its cathode. 
 
     
     
       2. The buck converter of  claim 1 , wherein said another switch comprises a shift control device operable to control a voltage across the voltage shifting capacitor. 
     
     
       3. The buck converter of  claim 2 , wherein the switch is a power MOSFET and the pulse width modulation signal is provided to a gate of the power MOSFET to turn the MOSFET on to connect the motor to the DC power source when desired. 
     
     
       4. The buck converter of  claim 3 , wherein the DC power supply is a battery. 
     
     
       5. The buck converter of  claim 4 , wherein the voltage shifting capacitor and the diode are connected across the switch such that current flows through the motor when the motor is not connected to the power supply by the switch. 
     
     
       6. The buck converter of  claim 5 , wherein the shift control device controls a rate of discharge of the voltage shifting capacitor. 
     
     
       7. The buck converter of  claim 6 , wherein the shift control device is an n-type MOSFET with a low threshold voltage. 
     
     
       8. A buck converter for use in controlling a motor, the buck converter comprising:
 a power input operable for connection to a DC power supply; 
 a switch for selectively connecting the motor to the power supply; 
 a pulse width modulation control operable to provide a pulse width modulation signal to the switch, wherein the switch connects the motor to the power supply based on the pulse width modulation signal; 
 a voltage shifting capacitor connected with an anode of a diode, said voltage shifting capacitor and said diode connected, in series, across said switch, and said diode connected to said motor only at its cathode; and 
 another switch directly connecting said anode of said diode to a ground terminal of said DC power supply; 
 wherein the voltage shifting capacitor acts as a voltage shifter that closes the motor path through a direct current (“DC”) line while the motor is in an OFF state. 
 
     
     
       9. The buck converter of  claim 8 , wherein said another switch comprises a shift control device operable to control a voltage across the voltage shifting capacitor to improve filtering. 
     
     
       10. The buck converter of  claim 9 , wherein the switch is a power MOSFET and the pulse width modulation signal is provided to a gate of the power MOSFET to turn the MOSFET on to connect the motor to the DC power source when desired. 
     
     
       11. The buck converter of  claim 10 , wherein the DC power supply is a battery. 
     
     
       12. The buck converter of  claim 11 , wherein the voltage shifting capacitor and the diode are connected across the switch such that current flows through the motor when the motor is not connected to the power supply by the switch. 
     
     
       13. The buck converter of  claim 12 , wherein the shift control device controls a rate of discharge of the voltage shifting capacitor. 
     
     
       14. The buck converter of  claim 13 , wherein the shift control device is an n-type MOSFET with a low threshold voltage. 
     
     
       15. A buck converter for use in controlling a motor, the buck converter comprising:
 a power input operable for connection to a DC power supply; 
 a switch for selectively connecting the motor to the power supply; 
 a pulse width modulation control operable to provide a pulse width modulation signal to the switch, wherein the switch connects the motor to the power supply based on the pulse width modulation signal; 
 a voltage shifting capacitor connected with an anode of a diode such that said voltage shifting capacitor and said diode are connected, in series, across said switch, and said diode is connected to said motor only at its cathode; and 
 another switch directly connecting said anode of said diode to a ground terminal of said DC power supply; 
 wherein current flows through the motor when the motor is not connected to the power supply by the switch. 
 
     
     
       16. The buck converter of  claim 15 , wherein said another switch comprises a shift control device operable to control a voltage across the voltage shifting capacitor. 
     
     
       17. The buck converter of  claim 16 , wherein the switch is a power MOSFET and the pulse width modulation signal is provided to a gate of the power MOSFET to turn the MOSFET on to connect the motor to the DC power source when desired. 
     
     
       18. The buck converter of  claim 17 , wherein the DC power supply is a battery. 
     
     
       19. The buck converter of  claim 18 , wherein the shift control device controls a rate of discharge of the voltage shifting capacitor. 
     
     
       20. The buck converter of  claim 19 , wherein the shift control device is an n-type MOSFET with a low threshold voltage.